Economic loss due to infectious diseases in the global aquaculture industry is estimated to be $3 billion annually. The aquaculture industry has the fastest growth rate of all animal producing food sectors; its contribution to the global food supply by weight has increased from 3.9% in 1970 to 32.4% in 2004, with a value of $70.3 billion. As the capture fishing industry has declined and wild stocks diminished, the aquaculture industry became an important source of food. Commercial catfish production accounts for 85 to 90% of the total finfish aquaculture production in the United States, with almost 300,000 tons produced annually. The most serious bacterial pathogens affecting this industry are Edwardsellia ictaluri and Flavobacterium columnare. Loss due to these bacterial pathogens is estimated to be $50-80 million, annually. In all kinds of intensive culture, where single or multiple species are reared in high density, infectious disease agents are easily transmitted between individuals. In those intensive systems, vaccination is one of the most important enhancers of production yields.
Currently, the most common method for vaccination in the aquaculture industry is intraperitoneal (i.p.) injection. This class of immunization is expensive due to labor intensity and added costs for anesthesia, gas, needles, electricity, etc. Furthermore, i.p. vaccination is cost prohibitive for booster immunizations. Consequently, injectable vaccines are not used in catfish aquaculture. Instead, live attenuated bacterial vaccines administered in a bath are commercially used. Live recombinant attenuated vaccines, which can protect against several diseases at low cost and are biologically contained, have not previously been designed for the aquaculture industry.